Hi Mahmoud, Welcome to the forum! I will make a few assumptions and you can correct me if I'm wrong. You want to use two TCs or one 3-wire RTD using the same circuit with no jumpers or switches. You really will find this difficult to achieve without some external jumpers or switches. Notice Figure 77 on page 52 of the ADS1220 datasheet. Note how the current sources connect directly to the RTD. If you drive the current through a series resistor you will quickly run into issues with drift and compliance voltage for the IDAC sources as there will be a voltage drop across the input resistors connected to the current source outputs. Depending on the operational temperature range, you may also see some leakage on AIN2 and AIN3 that may degrade your accuracy when connecting a TC to those inputs. For your RTD you may want to consider using a high-side reference and calculating your lead resistance and then subtracting from the measurement. This is demonstrated in the ADS122U04EVM user's guide in figure 16. The ADS122U04 is a similar device to the ADS1220 except the communications interface is UART instead of SPI and the leakage is also less on AIN3 as the low-side switch is removed. For your TC measurements you will need to compensate the cold-junction where the inputs connect to the PCB. You can use the internal temperature sensor of the ADS1220 , but routing becomes critical when trying to the place ADS1220 in the isolated thermal area for the inputs. You may want to take a look at the ADS124S08 (or ADS124S06 ). The ADS124S08EVM user's guide also has some example connections on how to connect various inputs to the device. Another device similar to the ADS1220 is the ADS1247 . The advantages of these devices are an included VBIAS for biasing a TC at mid-AVDD supply as well as self offset calibration. All of these devices can operate with bipolar supply with no degradation as compared to the unipolar supply. In all cases you would want to use a linear supply such as an LDO as opposed to a switching power supply to avoid additional noise. If a switcher must be used, then avoid switching frequencies that are multiples of the ADC modulator rate, and then use an LDO to regulate to the final voltage. If the TC is grounded to the machine, you must make sure that the TC output is within the operational range of the ADC input. You cannot assume that the machine ground is the same voltage potential as the ADC ground. For the ADS1220 , if the grounds are the same potential you will either need to use the bipolar supply mode if you want to use a gain greater than 4 or use PGA bypass mode (maximum gain of 4) when using a unipolar supply. Best regards, Bob B
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